Formation of SiN thin films

ABSTRACT

Methods of forming silicon nitride thin films on a substrate in a reaction space under high pressure are provided. The methods can include a plurality of plasma enhanced atomic layer deposition (PEALD) cycles, where at least one PEALD deposition cycle comprises contacting the substrate with a nitrogen plasma at a process pressure of 20 Torr to 500 Torr within the reaction space. In some embodiments the silicon precursor is a silyl halide, such as H2SiI2. In some embodiments the processes allow for the deposition of silicon nitride films having improved properties on three dimensional structures. For example, such silicon nitride films can have a ratio of wet etch rates on the top surfaces to the sidewall of about 1:1 in dilute HF.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/543,917, filed Aug. 19, 2019, which is a continuation of U.S.application Ser. No. 14/834,290, filed on Aug. 24, 2015, now U.S. Pat.No. 10,410,857, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND Field

The present disclosure relates generally to the field of semiconductordevice manufacturing and, more particularly, to low temperatureformation of silicon nitride thin films.

Description of the Related Art

Spacers are widely used in semiconductor manufacturing as structures toprotect against subsequent processing steps. For example, nitridespacers formed beside gate electrodes can be used as a mask to protectunderlying source/drain areas during doping or implanting steps.

As the physical geometry of semiconductor devices shrinks, the gateelectrode spacer becomes smaller and smaller. The spacer width islimited by the nitride thickness that can be deposited conformably overthe dense gate electrodes lines. Thus, the nitride spacer etchingprocess is preferred to have a high ratio of spacer width to nitridelayer thickness as deposited.

Current PEALD silicon nitride processes in general suffer fromanisotropic etch behavior when used to deposit on a three-dimensionalstructure, such as a trench structure. In other words, the filmdeposited on the sidewalls of a trench or fin or another threedimensional feature display inferior film properties as compared to filmon the top region of the feature. The film quality may be sufficient forthe target application on the top of the trench, or on planar regions ofa structured wafer, but not on the sidewalls or other non-horizontal orvertical surfaces.

FIGS. 1A and 1B illustrate a typical example of a silicon nitride film,which could be used, for example, in spacer applications. The film wasdeposited at 400° C. using a conventional PEALD process, not a processdescribed in the present application. FIG. 1A illustrates the film afterit was deposited on a three-dimensional surface but prior to beingetched by HF. An etching process was then performed by dipping theworkpiece in 0.5% HF for about 60 seconds. FIG. 1B illustrates theextent to which vertical portions of the silicon nitride film etch to agreater extent than the horizontal portions of the film. The filmthicknesses are indicated in nanometers. Structures such as these wouldnot generally survive further processing, such as in a FinFET spacerapplication.

SUMMARY

In some aspects, atomic layer deposition (ALD) methods of formingsilicon nitride films are provided. In some aspects, plasma enhancedatomic layer deposition (PEALD) methods of forming silicon nitride filmsare provided. The methods allow for the deposition of silicon nitridefilms with desirable qualities, such as good step coverage and patternloading effects, as well as desirable etch characteristics. According tosome embodiments, the silicon nitride films have a relatively uniformetch rate for both the vertical and the horizontal portions, whendeposited onto 3-dimensional structures. In some embodiments the wetetch rates of silicon nitride deposited on the vertical and horizontalportions of the three dimensional structure are approximately equal.Such three-dimensional structures may include, for example and withoutlimitation, FinFETS or other types of multiple gate FETs. In someembodiments, various silicon nitride films of the present disclosurehave an etch rate of less than half the thermal oxide removal rate ofabout 2-3 nm per minute with diluted HF (0.5%).

In some embodiments, methods of forming a silicon nitride thin film on asubstrate in a reaction space can include a plasma enhanced atomic layerdeposition (PEALD) process. The PEALD process may include at least onePEALD deposition cycle including contacting a surface of the substratewith a vapor phase silicon precursor to provide adsorbed silicon specieson the surface of the substrate and contacting the adsorbed siliconspecies with nitrogen plasma to form silicon nitride on the surface ofthe substrate. In some embodiments the silicon precursor is a siliconhalide. In some embodiments the silicon halide may comprise iodine, andmay be, for example H₂SiI₂. The pressure in the reaction space duringthe contacting steps can be at least about 20 Torr.

In some embodiments, the silicon nitride thin film is deposited on athree-dimensional structure on the substrate, and a wet etch rate ratioof a portion of the silicon nitride thin film formed on a top surface ofthe three-dimensional structure to a portion of the silicon nitride thinfilm formed on a sidewall surface of the three-dimensional structure isabout 1:1.

In some embodiments, the nitrogen plasma is formed using a plasma powerof about 500 Watts (W) to about 1000 W. In some embodiments, thecontacting steps are carried out at a process temperature of about 100°C. to about 650° C.

In some embodiments methods of forming a silicon nitride thin film on asubstrate in a reaction space can include a plurality of atomic layerdeposition (ALD) cycles. At least one of the ALD deposition cycles caninclude contacting a surface of the substrate with a vapor phase siliconprecursor to provide adsorbed silicon species on the surface of thesubstrate, and contacting the adsorbed silicon species with nitrogenreactants to form silicon nitride on the surface of the substrate. Thepressure in the reaction space during the contacting steps can be atleast about 20 Torr. In some embodiments, the process pressure withinthe reaction space is about 30 Torr to about 500 Torr. In someembodiments, the contacting steps can be carried out at a processtemperature of about 100° C. to about 650° C.

In some embodiments, the vapor phase silicon precursor can include asilyl halide. In some embodiments, the vapor phase silicon precursorcomprises iodine, and may be, for example, H₂SiI₂.

In some embodiments, the silicon nitride thin film is deposited on athree-dimensional structure on the surface of the substrate. A wet etchrate ratio of a portion of the silicon nitride thin film formed on a topsurface of the three-dimensional structure to a portion of the siliconnitride thin film formed on a sidewall surface of the three-dimensionalstructure can be about 1:1. In some embodiments,

In some embodiments, the at least one atomic layer deposition cyclecomprises a plasma enhanced atomic layer deposition (PEALD) cycle. Thenitrogen reactants can be generated by a plasma using a nitrogenprecursor. In some embodiments, the nitrogen plasma is formed fromnitrogen gas (N₂). In some embodiments, the nitrogen gas (N₂) flowscontinuously throughout the PEALD deposition cycle.

In some embodiments, excess vapor phase silicon precursors can beremoved between contacting the surface of the substrate with the vaporphase silicon precursor and contacting the adsorbed silicon species withthe nitrogen reactants. In some embodiments, a purge gas can be flowedbetween contacting the surface of the substrate with a vapor phasesilicon precursor and contacting the adsorbed silicon species with thenitrogen reactants.

In some embodiments, methods of forming a silicon nitride thin film on asubstrate in a reaction space can include a plurality of super-cyclesincluding a plurality of silicon nitride deposition sub-cyclescomprising alternately and sequentially contacting the substrate with asilicon precursor and a nitrogen plasma; and a plurality ofhigh-pressure treatment sub-cycles, where at least one of the pluralityof high-pressure treatment sub-cycles includes contacting the substratewith a nitrogen plasma at a pressure of greater than about 20 Torr. Insome embodiments, the pressure is about 20 Torr to about 500 Torr. Insome embodiments, the pressure is about 20 Torr to about 30 Torr. Insome embodiments the pressure is greater than 30 Torr, or between 30Torr and 500 Torr.

In some embodiments, the silicon precursor is H₂SiI₂. In someembodiments, the nitrogen-containing plasma is generated from a nitrogenprecursor selected from the group consisting of NH₃, N₂H₄, an N₂/H₂mixture, N₂, and any mixtures thereof.

In some embodiments, the silicon nitride thin film is deposited on athree-dimensional structure on the substrate. A wet etch rate ratio of awet etch rate of silicon nitride formed on a top surface of thethree-dimensional structure to a wet etch rate of the silicon nitrideformed on a sidewall surface of the three-dimensional structure is 1:1.

In some embodiments, the at least one silicon nitride depositionsub-cycle can include flowing a carrier gas throughout the at least onesilicon nitride deposition sub-cycle. In some embodiments, the at leastone silicon nitride deposition sub-cycle further includes flowing ahydrogen-containing gas and a nitrogen-containing gas throughout the atleast one silicon nitride deposition sub-cycle.

In some embodiments, the hydrogen-containing gas and thenitrogen-containing gas are used to form the nitrogen-containing plasma.In some embodiments, the at least one high-pressure treatment sub-cycleincludes flowing a carrier gas throughout the at least one high-pressuretreatment sub-cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIGS. 1A and 1B illustrate a silicon nitride film deposited by aconventional method and the results of an etching process performed onthe silicon nitride film;

FIG. 2A is a flow chart illustrating a method of forming a siliconnitride thin film by a high pressure PEALD process in accordance withsome embodiments of the present disclosure;

FIG. 2B is a flow chart illustrating a method of forming a siliconnitride thin film using a high-pressure treatment step in accordancewith some embodiments of the present disclosure.

FIGS. 3A and 3B are schematic diagrams showing exemplary ion incidentangles upon vertical surfaces of a three-dimensional structure of ionsgenerated by a lower pressure plasma and a higher pressure plasma,respectively.

FIGS. 4A and 4B are examples of timing diagrams for a silicon nitridedeposition process, according to some embodiments, comprising a siliconnitride deposition sub-cycle and a high-pressure treatment sub-cycle,respectively.

FIGS. 5A-5C show wet etch rate performance curves of a SiN film formedby a process using conventional pressure (FIG. 5A and FIG. 5B), and wetetch rate performance curves of a SiN film formed using a high-pressuretreatment process according to one or more embodiments described herein(FIG. 5C).

FIGS. 6A-6D are scanning electron microscope (SEM) images showingcross-sectional views of SiN films formed on trench structures prior toand after exposure of the films to a wet etch dip. FIGS. 6A and 6Billustrate conformality and wet etch of films formed using low pressure,while FIGS. 6C and 6D illustrate conformality and wet etch of filmsdeposited according to one or more embodiments described herein.

DETAILED DESCRIPTION

Silicon nitride films have a wide variety of applications, as will beapparent to the skilled artisan, such as in planar logic, DRAM, and NANDFlash devices. More specifically, conformal silicon nitride thin filmsthat display uniform etch behavior have a wide variety of applications,both in the semiconductor industry and also outside of the semiconductorindustry. According to some embodiments of the present disclosure,various silicon nitride films and precursors and methods for depositingthose films by atomic layer deposition (ALD) are provided. Importantly,in some embodiments the silicon nitride films have a relatively uniformetch rate for both vertical and horizontal portions, when deposited onto3-dimensional structures. Such three-dimensional structures may include,for example and without limitation, FinFETS or other types of multiplegate FETs. In some embodiments, various silicon nitride films of thepresent disclosure have an etch rate of less than half the thermal oxideremoval rate of about 2-3 nm per minute with diluted HF (0.5%).

In some embodiments, silicon nitride thin films are deposited on asubstrate by plasma-enhanced atomic layer deposition (PEALD) processes.In some embodiments a silicon nitride thin film is deposited over athree dimensional structure, such as a fin in the formation of a finFETdevice.

The formula of the silicon nitride films is generally referred to hereinas SiN for convenience and simplicity. However, the skilled artisan willunderstand that the actual formula of the silicon nitride, representingthe Si:N ratio in the film and excluding hydrogen or other impurities,can be represented as SiN_(x), where x varies from about 0.5 to about2.0, as long as some Si—N bonds are formed. In some cases, x may varyfrom about 0.9 to about 1.7, from about 1.0 to about 1.5, or from about1.2 to about 1.4. In some embodiments silicon nitride is formed where Sihas an oxidation state of +IV and the amount of nitride in the materialmight vary.

In some embodiments, a high pressure PEALD process is used to depositSiN thin films. A substrate on which the SiN film is to be deposited isalternately and sequentially contacted with a silicon precursor and anitrogen reactant, where the nitrogen reactant comprises reactivespecies generated by a plasma using a nitrogen precursor. The highpressure process can comprise a plurality of deposition cycles, whereinat least one deposition cycle is performed in an elevated pressureregime. For example, a deposition cycle of a high pressure PEALD processmay comprise alternately and sequentially contacting the substrate witha silicon precursor and a nitrogen reactant under the elevated pressure.In some embodiments, one or more deposition cycles of the PEALD processcan be performed at a process pressure of about 6 Torr to about 500Torr, about 6 Torr to about 50 Torr, or about 6 Torr to about 100 Torr.In some embodiments, the one or more deposition cycles can be performedat a process pressure of greater than about 20 Torr, including about 20Torr to about 500 Torr, about 30 Torr to about 500 Torr, about 40 Torrto about 500 Torr, or about 50 Torr to about 500 Torr. In someembodiments, the one or more deposition cycles can be performed at aprocess pressure of about 20 Torr to about 30 Torr, about 20 Torr toabout 100 Torr, about 30 Torr to about 100 Torr, about 40 Torr to about100 Torr or about 50 Torr to about 100 Torr.

In some embodiments, a high pressure PEALD process used to deposit SiNthin films can include one or more deposition cycles comprisingcontacting the substrate with the silicon precursor at a conventionalprocess pressure and contacting the silicon species adsorbed on thesubstrate with a nitrogen reactant, such as a nitrogen plasma, under anelevated pressure regime. For example, one or more deposition cycles ofa high pressure PEALD process may comprise contacting the substrate witha silicon precursor at a process pressure of about 0.1 Torr to about 5Torr, such as at about 3 Torr or lower, and contacting the adsorbedsilicon species with a nitrogen reactant at a process pressure of about6 Torr to about 500 Torr, about 20 Torr to about 500 Torr, about 30 Torrto about 500 Torr, about 40 Torr to about 500 Torr, or about 50 Torr toabout 500 Torr. In some embodiments, contacting the adsorbed siliconspecies with the nitrogen reactant can be performed at a processpressure of about 20 Torr to about 30 Torr, about 20 Torr to about 100Torr, about 30 Torr to about 100 Torr, about 40 Torr to about 100 Torror about 50 Torr to about 100 Torr.

In some embodiments, the high-pressure PEALD process may utilize a silylhalide as the silicon precursor. In some embodiments, the siliconprecursor comprises iodine. In some embodiments, the silicon precursoris H₂SiI₂.

In some embodiments the nitrogen precursor for the high-pressure PEALDprocess comprises nitrogen plasma. For example, the second precursor maycomprise N, NH or NH₂ radicals. In some embodiments the nitrogen plasmamay be generated from N₂, for example from a mixture of N₂ and H₂. Insome embodiments however, no hydrogen plasma is utilized. Nitrogenplasma may be generated, for example, at a power of about 10 W to about2,000 W, about 50 W to about 1000 W, about 100 W to about 1000 W orabout 500 W to about 1000 W. For example, the nitrogen plasma can begenerated at a power of about 800 W to about 1000 W.

In some embodiments, the high-pressure PEALD process can be performed ata process temperature of about 100° C. to about 650° C. In someembodiments the PEALD process can be performed at a process temperatureof about 100° C. to about 550° C. or about 100° C. to about 450° C.

For example, in some embodiments, each of a plurality of depositioncycles of a high-pressure PEALD process may be performed in the elevatedpressure regime of about 6 Torr to about 500 Torr, preferably about 20Torr to about 500 Torr, and more preferably about 30 Torr to about 500Torr, at a temperature of about about 100° C. to about 650° C., andusing a silyl halide, such as H₂SiI₂ as the silicon precursor. In someembodiments at least one of the plurality of deposition cycles isperformed under these conditions. For example, one or more high pressuredeposition cycles may be performed intermittently during deposition of asilicon nitride film, with the remaining deposition cycles beingperformed at conventional pressure.

SiN thin films formed on three-dimensional structures using suchdeposition processes can advantageously demonstrate desired uniformityin characteristics between portions of the films formed on horizontalsurfaces (e.g., top surfaces) and vertical surfaces (e.g., sidewallsurfaces) of the structure. For example, SiN thin films formed usingsuch PEALD processes can advantageously demonstrate increased uniformityin wet etch rates (WER), film thicknesses, density, and/or purity,between SiN film formed on horizontal surfaces and vertical surfaces ofa three-dimensional structure. In some embodiments, such a PEALD processcan advantageously provide SiN thin films having desired wet etch rateratios (WERR). As used herein, a wet etch rate ratio refers to a ratioof an etch rate of SiN film formed on a horizontal surface (e.g., a topsurface) to an etch rate of the SiN film formed on a vertical surface(e.g., a sidewall surface). For example, a wet etch rate of SiN thinfilm deposited using a high-pressure PEALD process described herein candemonstrate the same or substantially the same WER on both vertical andhorizontal surfaces, for example providing a wet etch rate ratio (WERR)of about 1 when exposed to dilute HF (0.5 weight % aqueous solution). Insome embodiments, the ratio can be about 0.25 to about 2, about 0.5 toabout 1.5, about 0.75 to about 1.25, or about 0.9 to about 1.1. In someembodiments, these ratios can be achieved in aspect ratios of more thanabout 2, preferably in aspect ratios more than about 3, more preferablyin aspect ratios more than about 5 and most preferably in aspect ratiosmore than about 8. In some embodiments, such a PEALD process canadvantageously provide SiN thin films having the same or substantiallythe same thickness on both vertical and horizontal surfaces. Withoutwishing to be held to any particular theory, it is believed that in someembodiments, a SiN PEALD process performed in an elevated pressureregime may advantageously reduce anisotropy of ion bombardment byincreasing collision between the ions of the plasma, thereby reducingdifferences in one or more characteristics of SiN film formed onhorizontal and vertical surfaces of a three-dimensional structure.

In some embodiments, SiN can be deposited using at least one lowerpressure deposition cycle, and subsequently treated by a high-pressuretreatment process, to provide SiN thin films having desiredcharacteristics. In some embodiments, a process for forming SiN thinfilms can include one or more silicon nitride deposition sub-cycles andone or more high-pressure treatment sub-cycles. In some embodiments, theone or more silicon nitride deposition sub-cycles deposits SiN on thesubstrate at conventional pressure and the one or more high-pressuretreatment sub-cycles can be provided intermittently and advantageouslyimprove one or more characteristics of the deposited SiN to provide aSiN thin film having one or more desired characteristics, such as animproved wet etch rate ratio. The high pressure treatment sub-cycle canbe provided after each silicon nitride deposition sub-cycle, orintermittently, such as at regular intervals during the depositionprocess, for example after every 2, 3, 4, 5, 10, 20 etc. . . . cycles.

A silicon nitride deposition sub-cycle may comprise a PEALD processperformed at a conventional deposition pressure, followed by ahigh-pressure treatment process comprising a plasma step performed at apressure significantly higher than the conventional deposition pressure.For example, the PEALD process can be performed at a process pressure ofabout 0.1 Torr to about 5 Torr, such as at about 3 Torr or lower orabout 4 Torr or lower, and the high-pressure treatment sub-cycle can beperformed at a process pressure of at least about 6 Torr, such as atleast about 7 Torr, at least about 20 Torr, at least about 30 Torr, orat least about 40 Torr, including about 6 Torr to about 500 Torr, about7 Torr to about 500 Torr, about 20 Torr to about 500 Torr, about 30 Torrto about 500 Torr, about 40 Torr to about 500 Torr, about 6 Torr toabout 100 Torr, about 50 Torr to about 100 Torr, about 40 Torr to about100 Torr, about 30 Torr to about 100 Torr, or about 20 Torr to about 100Torr.

In some embodiments, the PEALD process may use a silyl halide, forexample comprising iodine, such as H₂SiI₂, as a silicon precursor incombination with a nitrogen precursor, such as a nitrogen plasma. Thehigh-pressure treatment process may comprise providing nitrogen plasmaat the elevated pressure. In some embodiments, such a silicon nitrideformation process can unexpectedly allow formation of conformal SiNfilms on three-dimensional structures having desired filmcharacteristics on both vertical and horizontal surfaces. For example,such a silicon nitride formation process may unexpectedly reducedifferences in quality between thin film formed on vertical andhorizontal surfaces, including differences between wet etch rates (WER)and/or film thicknesses, while also providing a film having desiredimpurity levels. In some embodiments, such a silicon nitride formationprocess can advantageously provide SiN thin films having the same orsubstantially the same WER on both vertical and horizontal surfaces. Insome embodiments, such a silicon nitride formation process canadvantageously provide SiN thin films having the same or substantiallythe same thickness on both vertical and horizontal surfaces. In someembodiments, such a silicon nitride formation process can advantageouslyprovide SiN thin films having desired uniformity in film density and/orimpurity levels on both vertical and horizontal surfaces. For example, aratio of a wet etch rate of a portion of the SiN thin formed onhorizontal surfaces (e.g., top surfaces) of a three-dimension structureto that of a portion of the SiN film formed on vertical surfaces (e.g.,sidewall surfaces) when exposed to dilute HF (0.5 weight % aqueoussolution) can be about 1. In some embodiments, the ratio can be about0.25 to about 2, about 0.5 to about 1.5, about 0.75 to about 1.25, orabout 0.9 to about 1.1. These ratios can be achieved in aspect ratios,for example, of more than about 2, preferably in aspect ratios more thanabout 3, more preferably in aspect ratios more than about 5 and mostpreferably in aspect ratios more than about 8.

In some embodiments, a process for forming silicon nitride thin filmscan include one or more super cycles, each of the one or moresuper-cycles including one or more silicon nitride deposition sub-cyclesand one or more high-pressure treatment sub-cycles. A super-cycle mayinclude the one or more silicon nitride deposition sub-cycles followedby the one or more high-pressure treatment sub-cycles. In someembodiments, the super-cycle can be repeated a number of times to form asilicon nitride thin film of a desired thickness and having one or moredesired characteristics. In some embodiments, the number of siliconnitride deposition sub-cycles and the number of high-pressure treatmentsub-cycles of one super-cycle can be different from one or more othersuper cycles of a silicon nitride formation process comprising aplurality of super-cycles. In some embodiments, the number of siliconnitride deposition sub-cycles and the number of high-pressure treatmentsub-cycles of one super-cycle can the same as one or more other supercycles of a silicon nitride formation process comprising a plurality ofsuper-cycles. In some embodiments, a process for forming a siliconnitride film can include one super cycle, the super cycle including anumber of silicon nitride deposition sub-cycles followed by a number ofhigh-pressure treatment sub-cycles. The number of super cycles, and/orsilicon nitride deposition sub-cycles and high-pressure treatmentsub-cycles in a super cycle, can be selected to form a silicon nitridefilm having desired properties. As described herein, one or moreprocesses described herein can provide a conformal SiN thin film over athree-dimensional structure, the SiN thin film formed on thethree-dimensional structure also demonstrating desired uniformity incharacteristics on both vertical and horizontal surfaces.

Formation of Silicon Nitride Thin Films

FIG. 2A is a flow chart generally illustrating a silicon nitride PEALDdeposition cycle 200 performed under an elevated process pressure thatcan be used to deposit a silicon nitride thin film in accordance withsome embodiments. According to certain embodiment, a silicon nitridethin film is formed on a substrate by a high-pressure PEALD-type processcomprising multiple silicon nitride deposition cycles, each siliconnitride deposition cycle 200 comprising:

(1) contacting a surface of a substrate with vaporized silicon precursorunder an elevated process pressure 202 such that silicon species adsorbonto the surface of the substrate;

(2) contacting the adsorbed silicon species with nitrogen-containingreactants under the elevated process pressure 204, thereby convertingthe adsorbed silicon species into silicon nitride.

In some embodiments, the nitrogen-containing reactants comprisesreactants generated by a plasma from one or more nitrogen-containingprecursors.

In some embodiments, the one or more nitrogen precursors may flowcontinuously throughout the cycle, with the nitrogen-containing plasmaformed at the appropriate times to convert adsorbed silicon species intosilicon nitride. For example, nitrogen gas (N₂) and/or hydrogen gas (H₂)may flow continuously throughout the cycle.

The contacting steps are repeated until a thin film of a desiredthickness and composition is obtained. Excess reactants may be purgedfrom the reaction space after each contacting step, i.e., steps 202 and204.

In some embodiments, the silicon precursor of PEALD deposition cycle 200may comprise a silyl halide. In some embodiments, the silicon precursoris H₂SiI₂.

In some embodiments, the high pressure PEALD process is performed at atemperature from about 100° C. to about 650° C., about 100° C. to about550° C., about 100° C. to about 450° C., or about 200° C. to about 600°C. In some embodiments the temperature is about 300° C., or about 550°C. In some embodiments the temperature is about 400° C. to about 500° C.In some embodiments, the high pressure PEALD process is performed at atemperature of about 550° C. or about 600° C.

In some embodiments, one or both of the contacting steps (1) and (2)described with reference to FIG. 2A can be followed by a step in whichexcess reactants and/or reaction byproducts, if any, are removed fromthe vicinity of the substrate. For example, a purge step can follow oneor both of the contacting steps (1) and (2).

As will be described in further details below, the high-pressure PEALDprocess for depositing the silicon nitride thin film can be performed ata process pressure of greater than about 6 Torr, or about 20 Torr. Insome embodiments, the process pressure can be performed at a pressure ofabout 6 Torr to about 500 Torr, about 6 Torr to about 100 Torr, about 40Torr to about 500 Torr, about 50 Torr to about 100 Torr, about 40 Torrto about 100 Torr, about 30 Torr to about 100 Torr, or about 20 Torr toabout 100 Torr. In some embodiments, the process pressure can be about20 Torr to about 50 Torr, or about 20 Torr to about 30 Torr. Forexample, one or more of the PEALD deposition cycles of the high-pressurePEALD process can be performed at a process pressure of about 20 Torr toabout 500 Torr, including about 30 Torr to about 500 Torr. In someembodiments, the contacting steps (1) and (2) described with referenceto FIG. 2A can be performed at such elevated pressures.

As will be described in further details below, the nitrogen-containingplasma described with reference to FIG. 2A can be generated usingnitrogen-containing gas, including gas comprising compounds having bothN and H, such as NH₃ and N₂H₄, a mixture of N₂/H₂ or other precursorshaving an N—H bond. In some embodiments, a plasma power used forgenerating the nitrogen-containing plasma can be about 10 Watts (W) toabout 2,000 W, about 50 W to about 1000 W, about 100 W to about 1000 Wor about 500 W to about 1000 W. In some embodiments, a plasma power usedfor generating the nitrogen-containing plasma can be about 800 W toabout 1,000 W.

As described herein, in some embodiments, one or more deposition cyclesor portions of a deposition cycle of a PEALD process for forming SiN canbe performed at two different process pressures. In some embodiments,contacting the substrate with the silicon precursor can be performed ata process pressure of about 0.01 Torr to about 5 Torr, including about0.1 Torr to about 5 Torr or about 1 Torr to about 5 Torr, whilecontacting the adsorbed silicon species can be performed under anelevated pressure regime as described herein. For example, contactingthe adsorbed silicon species with nitrogen reactants can be performed ata process pressure of at least about 6 Torr, about 7 Torr, about 20Torr, about 30 Torr or about 40 Torr. In some embodiments, the processpressure can be about 6 Torr to about 500 Torr, about 7 Torr to about500 Torr, about 20 to about 500 Torr, about 6 Torr to about 100 Torr,about 20 Torr to about 100 Torr, or about 30 Torr to about 100 Torr.

Referring to FIG. 2B, a flow chart generally illustrating a process forforming silicon nitride thin film according to another embodiment isshown. As described herein, in some embodiments, a process for forming asilicon nitride thin film can include one or more super-cycles 220,where each of the one or more super-cycles includes one or more siliconnitride deposition sub-cycles 226 and one or more high-pressuretreatment sub-cycles 228. According to certain embodiment, a siliconnitride deposition sub-cycle 226 may comprise a PEALD processcomprising:

(1) contacting a surface of a substrate with vaporized siliconprecursors 222 such that silicon species adsorb onto the surface of thesubstrate;

(2) contacting the adsorbed silicon species with nitrogen reactants 204,thereby converting the adsorbed silicon compound into silicon nitride.

In some embodiments, the silicon nitride deposition sub-cycle 226 isperformed at a process pressure of about 0.01 Torr to about 5 Torr,preferably from about 0.1 Torr to about 5 Torr, and more preferably fromabout 1 Torr to about 5 Torr. The one or more silicon nitride depositionsub-cycles 226 can be performed at a pressure significantly less thanthat applied in the PEALD process described with reference to FIG. 2A.

In some embodiments, the silicon precursor of the silicon nitridedeposition sub-cycle 226 may comprise a silyl halide. In someembodiments, the silicon precursor is H₂SiI₂.

In some embodiments, the silicon nitride deposition sub-cycle 226 isperformed at a temperature from about 100° C. to about 650° C., about100° C. to about 550° C., about 100° C. to about 450° C., about 200° C.to about 600° C., about 300° C. and about 550° C., or at about 400° C.to about 500° C. In some embodiments, the silicon nitride depositionsub-cycle 226 is performed at a temperature of about 550° C. or about600° C. The silicon nitride deposition sub-cycle 226 may be repeated anumber of times to provide desired deposition of SiN.

As shown in FIG. 2B, the super-cycle 220 can include one or morehigh-pressure treatment sub-cycles 228. In some embodiments, the siliconnitride deposition sub-cycle 226 can be repeated a number of times ineach of the one or more super-cycles 220 prior to performing one or morehigh-pressure treatment sub-cycles 228. The one or more high-pressuretreatment sub-cycles 228 can be configured to improve one or morecharacteristics of the SiN deposited using the one or more siliconnitride deposition sub-cycles 226.

As will be described in further details below, a high-pressure treatmentsub-cycle can include one or more plasma steps performed in an elevatedpressure regime, such as a pressure of greater than about 6 Torr, about20 Torr, about 30 Torr or about 50 Torr. In some embodiments, the plasmastep can be performed at a pressure of about 20 Torr to about 500 Torr.In some embodiments, the one or more plasma steps can comprise anitrogen-containing plasma free or substantially free ofhydrogen-containing species. For example, the nitrogen-containing plasmacan be generated using gas free or substantially free of hydrogen. Forexample, hydrogen-containing gas (e.g., hydrogen (H₂) gas) is not flowedto the reaction chamber during the one or more plasma steps of thehigh-pressure treatment sub-cycles 228. In some embodiments, thenitrogen-containing plasma is generated using nitrogen gas (N₂). In someembodiments, the high-pressure treatment sub-cycles 228 is performed ata temperature between about 100° C. to about 650° C., 100° C. to about550° C., about 100° C. to about 450° C., about 200° C. to about 400° C.,about 300° C. and about 400° C., or at about 400° C. A plasma power fora plasma step in a high-pressure treatment sub-cycle 228 can be about100 Watts (W) to about 1,500 W, preferably from about 200 W to about1,000 W, more preferably from about 500 W to about 1,000 W. For example,a high-pressure treatment process may have a plasma power of about 800W.

PEALD of Silicon Nitride

As described herein, in some embodiments, a process for forming SiN thinfilms can be a PEALD process performed in an elevated process pressureregime. The process pressure for a high-pressure PEALD process can begreater than about 6 Torr, including greater than about 20 Torr, about30 Torr or about 50 Torr. In some embodiments, the process pressure fora high-pressure PEALD process can be about 20 Torr to about 500 Torr,including about 30 Torr to about 500 Torr, about 20 Torr to about 100Torr, 30 Torr to about 100 Torr, about 20 Torr to about 50 Torr, orabout 30 Torr to about 50 Torr. In some embodiments, a process forforming SiN thin films can comprise a plurality of super-cycles whichcan include one or more silicon nitride deposition sub-cycles comprisingPEALD processes performed at lower process pressures for depositing SiNin combination with one or more high pressure treatment sub-cycles. Forexample, PEALD processes for the one or more silicon nitride depositionsub-cycles can comprise a process pressure of about 0.01 Torr to about 5Torr, preferably from about 0.1 Torr to about 3 Torr, and the one ormore high-pressure treatment sub-cycles can comprise a process pressureof greater than about 20 Torr, including greater than about 30 Torr orabout 50 Torr.

PEALD processes can be used to deposit SiN on substrates such asintegrated circuit workpieces, and in some embodiments onthree-dimensional structures on the substrates. Briefly, a substrate orworkpiece is placed in a reaction chamber and subjected to alternatelyrepeated surface reactions. In some embodiments, thin SiN films areformed by repetition of a self-limiting ALD cycle. ALD-type processesare based on controlled, generally self-limiting surface reactions. Gasphase reactions are typically avoided by contacting the substratealternately and sequentially with the reactants. Vapor phase reactantsare separated from each other in the reaction chamber, for example, byremoving excess reactants and/or reactant byproducts between reactantpulses. The reactants may be removed from proximity of the substratesurface with the aid of a purge gas and/or vacuum. In some embodimentsexcess reactants and/or reactant byproducts are removed from thereaction space by purging, for example with an inert gas.

Preferably, for depositing SiN films, each ALD cycle comprises at leasttwo distinct phases. The provision and removal of a reactant from thereaction space may be considered a phase. In a first phase, a firstreactant comprising silicon is provided and forms no more than about onemonolayer on the substrate surface. This reactant is also referred toherein as “the silicon precursor,” “silicon-containing precursor,” or“silicon reactant” and may be, for example, H₂SiI₂.

In a second phase, a second reactant comprising a reactive species isprovided and may convert adsorbed silicon to silicon nitride. In someembodiments the second reactant comprises a nitrogen reactant. In someembodiments, the reactive species comprises an excited species. In someembodiments the second reactant comprises a species from a nitrogencontaining plasma. For example, the second reactant may comprisenitrogen-containing reactants generated by plasma from one or morenitrogen precursors. In some embodiments, the second reactant comprisesnitrogen radicals, nitrogen atoms and/or nitrogen plasma. The secondreactant may comprise other species that are not nitrogen-containingreactants. In some embodiments, the second reactant may comprise aplasma of hydrogen, radicals of hydrogen, or atomic hydrogen in one formor another. In some embodiments, the second reactant may comprise aspecies from a noble gas, such as He, Ne, Ar, Kr, or Xe, preferably Aror He, for example as radicals, in plasma form, or in elemental form.These reactive species from noble gases do not necessarily contributematerial to the deposited film, but can in some circumstances contributeto film growth as well as help in the formation and ignition of plasma.In some embodiments a gas that is used to form a plasma may flowconstantly throughout the deposition process but only be activatedintermittently. In some embodiments, the second reactant does notcomprise a species from a noble gas, such as Ar. Thus, in someembodiments the adsorbed silicon precursor is not contacted with areactive species generated by a plasma from Ar.

Additional phases may be added and phases may be removed as desired toadjust the composition of the final film.

One or more of the reactants may be provided with the aid of a carriergas, such as one or more noble gases. In some embodiments, the carriergas comprises one or more of Ar and He. In some embodiments the siliconprecursor and the second reactant are provided with the aid of a carriergas.

In some embodiments, two of the phases may overlap, or be combined. Forexample, the silicon precursor and the second reactant may be providedsimultaneously in pulses that partially or completely overlap. Inaddition, although referred to as the first and second phases, and thefirst and second reactants, the order of the phases may be varied, andan ALD cycle may begin with any one of the phases. That is, unlessspecified otherwise, the reactants can be provided in any order, and theprocess may begin with any of the reactants.

According to some embodiments, a silicon nitride thin film is depositedusing a PEALD process on a substrate having three-dimensional features,such as in a FinFET application. The process may comprise the followingsteps:

(1) a substrate comprising a three-dimensional structure is provided ina reaction space;

(2) contacting the substrate with a silicon-containing precursor, suchas SiI₂H₂, so that silicon-containing species are adsorbed to a surfaceof the substrate, including onto surfaces of the three-dimensionalstructure;

(3) excess silicon-containing precursor and reaction byproducts areremoved from the reaction space;

(4) contacting the adsorbed silicon species with nitrogen-containingspecies, where the nitrogen-containing species are formed by generatinga nitrogen-containing plasma using vapor phase reactants, such as N₂,NH₃, N₂H₄, or N₂ and H₂; and

(5) removing excess nitrogen atoms, plasma, or radicals and reactionbyproducts;

Steps (2) through (5) may be repeated until a silicon nitride film of adesired thickness is formed.

In some embodiments step (4) can be replaced by a step in which thenitrogen atoms, plasma or radicals are formed remotely and provided tothe reaction space.

In some embodiments, the PEALD process is performed at a temperaturebetween about 100° C. to about 650° C., about 100° C. to about 550° C.,about 100° C. to about 450° C., about 200° C. to about 600° C., or atabout 400° C. to about 500° C. In some embodiments the temperature isabout 300° C. In some embodiments, the PEALD process is performed at atemperature of about 550° C. or about 600° C.

As discussed in more detail below, in some embodiments for depositing aSiN film, one or more PEALD deposition cycles begin with provision ofthe silicon precursor, followed by the second precursor. In otherembodiments deposition may begin with provision of the second precursor,followed by the silicon precursor. One of skill in the art willrecognize that the first precursor phase generally reacts with thetermination left by the last phase in the previous cycle. Thus, while noreactant may be previously adsorbed on the substrate surface or presentin the reaction space if the reactive species phase is the first phasein the first PEALD cycle, in subsequent PEALD cycles the reactivespecies phase will effectively follow the silicon phase. In someembodiments one or more different PEALD sub-cycles are provided in theprocess for forming a SiN thin film.

Excess reactant and reaction byproducts, if any, are removed from thevicinity of the substrate, and in particular from the substrate surface,between reactant pulses. In some embodiments the reaction chamber ispurged between reactant pulses, such as by purging with an inert gas.The flow rate and time of each reactant, is tunable, as is the removalstep, allowing for control of the quality and various properties of thefilms.

As mentioned above, in some embodiments a gas is provided to thereaction chamber continuously during each deposition cycle, and reactivespecies are provided by generating a plasma in the gas, either in thereaction chamber or upstream of the reaction chamber. In someembodiments the gas comprises nitrogen. In some embodiments the gas isnitrogen. In other embodiments the gas may comprise helium, or argon. Insome embodiments the gas is helium or nitrogen. The flowing gas may alsoserve as a purge gas for the first and/or second reactant (or reactivespecies). For example, flowing nitrogen may serve as a purge gas for afirst silicon precursor and also serve as a second reactant (as a sourceof reactive species). In some embodiments, nitrogen, argon, or heliummay serve as a purge gas for a first precursor and a source of excitedspecies for converting the silicon precursor to the silicon nitridefilm. In some embodiments the gas in which the plasma is generated doesnot comprise argon and the adsorbed silicon precursor is not contactedwith a reactive species generated by a plasma from Ar.

The PEALD deposition cycle is repeated until a SiN film of the desiredthickness and composition is obtained. In some embodiments thedeposition parameters, such as the flow rate, flow time, purge time,and/or reactants themselves, may be varied in one or more depositionsub-cycles in order to obtain a film with the desired characteristics.In some embodiments, hydrogen and/or hydrogen plasma are not provided ina deposition sub-cycle, or in the deposition process.

The term “pulse” may be understood to comprise feeding reactant into thereaction chamber for a predetermined amount of time. The term “pulse”does not restrict the length or duration of the pulse and a pulse can beany length of time.

In some embodiments, the silicon reactant is provided first. After aninitial surface termination, if necessary or desired, a first siliconreactant pulse is supplied to the workpiece. In accordance with someembodiments, the first reactant pulse comprises a carrier gas flow and avolatile silicon species, such as H₂SiI₂, that is reactive with theworkpiece surfaces of interest. Accordingly, the silicon reactantadsorbs upon these workpiece surfaces. The first reactant pulseself-saturates the workpiece surfaces such that any excess constituentsof the first reactant pulse do not further react with the molecularlayer formed by this process.

The first silicon reactant pulse is preferably supplied in gaseous form.The silicon precursor gas is considered “volatile” for purposes of thepresent description if the species exhibits sufficient vapor pressureunder the process conditions to transport the species to the workpiecein sufficient concentration to saturate exposed surfaces.

In some embodiments the silicon reactant pulse is from about 0.05seconds to about 5.0 seconds, about 0.1 seconds to about 3 seconds orabout 0.2 seconds to about 1.0 seconds. The optimum pulsing time can bereadily determined by the skilled artisan based on the particularcircumstances.

After sufficient time for a molecular layer to adsorb on the substratesurface, excess first silicon reactant is then removed from the reactionspace. In some embodiments the excess first reactant is purged bystopping the flow of the first chemistry while continuing to flow acarrier gas or purge gas for a sufficient time to diffuse or purgeexcess reactants and reactant by-products, if any, from the reactionspace. In some embodiments the excess first precursor is purged with theaid of inert gas, such as nitrogen or argon, that is flowing throughoutthe sub-cycle.

In some embodiments, the first reactant is purged for about 0.1 secondsto about 10 seconds, about 0.3 seconds to about 5 seconds or about 0.3seconds to about 1 second. Provision and removal of the silicon reactantcan be considered the first or silicon phase of a PEALD process.

In the second phase, a second reactant comprising a reactive species,such as nitrogen plasma is provided to the workpiece. Nitrogen, N₂, isflowed continuously to the reaction chamber during each ALD cycle insome embodiments. Nitrogen plasma may be formed by generating a plasmain nitrogen in the reaction chamber or upstream of the reaction chamber,for example by flowing the nitrogen through a remote plasma generator.

In some embodiments, plasma is generated in flowing H₂ and N₂ gases. Insome embodiments the H₂ and N₂ are provided to the reaction chamberbefore the plasma is ignited or nitrogen and hydrogen atoms or radicalsare formed. Without being bound to any theory, it is believed that thehydrogen may have a beneficial effect on the ligand removal step i.e. itmay remove some of the remaining ligands or have other beneficialeffects on the film quality. In some embodiments the H₂ and N₂ areprovided to the reaction chamber continuously and nitrogen and hydrogencontaining plasma, atoms or radicals is created or supplied when needed.

In some embodiments, the nitrogen-containing plasma does not orsubstantially does not comprise hydrogen-containing species. Forexample, the nitrogen-containing plasma is generated using gas free orsubstantially free of hydrogen-containing species. In some embodimentsthe entire SiN deposition is done is hydrogen free. However, in someembodiments a plasma comprising H-species can be used during a highpressure step.

Typically, the second reactant, for example comprising nitrogen plasma,is provided for about 0.1 seconds to about 10 seconds. In someembodiments the second reactant, such as nitrogen plasma, is providedfor about 0.1 seconds to about 10 seconds, 0.5 seconds to about 5seconds or 0.5 seconds to about 2.0 seconds. However, depending on thereactor type, substrate type and its surface area, the second reactantpulsing time may be even higher than about 10 seconds. In someembodiments, pulsing times can be on the order of minutes. The optimumpulsing time can be readily determined by the skilled artisan based onthe particular circumstances.

In some embodiments the second reactant is provided in two or moredistinct pulses, without introducing another reactant in between any ofthe two or more pulses. For example, in some embodiments a nitrogenplasma is provided in two or more, preferably in two, sequential pulses,without introducing a Si-precursor in between the sequential pulses. Insome embodiments during provision of nitrogen plasma two or moresequential plasma pulses are generated by providing a plasma dischargefor a first period of time, extinguishing the plasma discharge for asecond period of time, for example from about 0.1 seconds to about 10seconds, from about 0.5 seconds to about 5 seconds or about 1.0 secondsto about 4.0 seconds, and exciting it again for a third period of timebefore introduction of another precursor or a removal step, such asbefore the Si-precursor or a purge step. Additional pulses of plasma canbe introduced in the same way. In some embodiments a plasma is ignitedfor an equivalent period of time in each of the pulses.

Nitrogen plasma may be generated by applying RF power of from about 10 Wto about 2000 W, preferably from about 50 W to about 1000 W, morepreferably from about 500 W to about 1000 W in some embodiments. In someembodiments the RF power density may be from about 0.02 W/cm² to about2.0 W/cm², preferably from about 0.05 W/cm² to about 1.5 W/cm². The RFpower may be applied to nitrogen that flows during the nitrogen plasmapulse time, that flows continuously through the reaction chamber, and/orthat flows through a remote plasma generator. Thus in some embodimentsthe plasma is generated in situ, while in other embodiments the plasmais generated remotely. In some embodiments a showerhead reactor isutilized and plasma is generated between a susceptor (on top of whichthe substrate is located) and a showerhead plate. In some embodimentsthe gap between the susceptor and showerhead plate is from about 0.1 cmto about 20 cm, from about 0.5 cm to about 5 cm, or from about 0.8 cm toabout 3.0 cm.

After a time period sufficient to completely saturate and react thepreviously adsorbed molecular layer with the nitrogen plasma pulse, anyexcess reactant and reaction byproducts are removed from the reactionspace. As with the removal of the first reactant, this step may comprisestopping the generation of reactive species and continuing to flow theinert gas, such as nitrogen or argon for a time period sufficient forexcess reactive species and volatile reaction by-products to diffuse outof and be purged from the reaction space. In other embodiments aseparate purge gas may be used. The purge may, in some embodiments, befrom about 0.1 seconds to about 10 seconds, about 0.1 seconds to about 4seconds or about 0.1 seconds to about 0.5 seconds. Together, thenitrogen plasma provision and removal represent a second, reactivespecies phase in a silicon nitride atomic layer deposition cycle.

According to some embodiments of the present disclosure, PEALD reactionsmay be performed at temperatures as discussed above, for example,ranging from about 25° C. to about 700° C., from about 50° C. to about600° C., from about 100° C. to about 600° C., from about 200° C. toabout 600° C., from about 100° C. to about 450° C., or from about 200°C. to about 400° C. In some embodiments the temperature may be about 300c, about 550° C. or about 400 to about 500° C. In some embodiments, theoptimum reactor temperature may be limited by the maximum allowedthermal budget. Therefore, in some embodiments the reaction temperatureis from about 300° C. to about 400° C. In some applications, the maximumtemperature is about 400° C., and, therefore the PEALD process is run atthat reaction temperature.

In some embodiments, the exposed surfaces of the workpiece can bepretreated to provide reactive sites to react with the first phase ofthe PEALD sub-cycle. In some embodiments a separate pretreatment step isnot performed. In some embodiments the substrate is pretreated toprovide a desired surface termination. In some embodiments the substrateis pretreated with plasma.

In some embodiments the substrate on which deposition is desired, suchas a semiconductor workpiece, is loaded into a reactor. The reactor maybe part of a cluster tool in which a variety of different processes inthe formation of an integrated circuit are carried out. In someembodiments a flow-type reactor is utilized. In some embodiments ashower head type of reactor is utilized. In some embodiments, a spacedivided reactor is utilized. In some embodiments a high-volumemanufacturing-capable single wafer PEALD reactor is used. In otherembodiments a batch reactor comprising multiple substrates is used. Forembodiments in which batch PEALD reactors are used, the number ofsubstrates is preferably in the range of 10 to 200, more preferably inthe range of 50 to 150, and most preferably in the range of 100 to 130.

Exemplary single wafer reactors, designed specifically to enhance PEALDprocesses, are commercially available from ASM America, Inc. (Phoenix,Ariz.) under the tradenames Pulsar® 2000 and Pulsar® 3000 and ASM JapanK.K (Tokyo, Japan) under the tradename Eagle® XP, XP8 and Dragon®.Exemplary batch PEALD reactors, designed specifically to enhance PEALDprocesses, are commercially available from and ASM Europe B.V (Almere,Netherlands) under the tradenames A400™ and A412™.

High-Pressure Treatment Sub-Cycle

As described herein, according to some embodiments, a process forforming SiN thin films can include one or more super-cycles comprisingone or more SiN deposition cycles carried out at conventional pressureand one or more high-pressure treatment sub-cycles. As used herein, ahigh-pressure treatment sub-cycle refers to a treatment sub-cyclecomprising a process pressure of at least about 6 Torr for at least aportion of the sub-cycle, including at least about 7 Torr, at leastabout 20 Torr, about 30 Torr, about 40 Torr, or about 50 Torr. In someembodiments, the high-pressure treatment sub-cycle comprises a plasmastep performed at a process pressure of at least about 20 Torr. Forexample, a pressure within the reaction chamber to which the substrateis exposed during the plasma step may be at least about 20 Torr for atleast a portion of plasma step, including at least about 30 Torr, about40 Torr, or about 50 Torr. In some embodiments, the pressure within thereaction chamber to which the substrate is exposed during the plasmastep may be up to about 50 Torr, up to about 100 Torr or up to about 500Torr. For example, the pressure within the reaction chamber can be about6 Torr to about 50 Torr, 20 Torr to about 50 Torr, 6 Torr to about 500Torr, or about 20 Torr to about 500 Torr for the entire or substantiallyentire plasma step. In some embodiments, a process pressure of a plasmastep in the high-pressure treatment sub-cycle can be about 30 Torr toabout 500 Torr, about 40 Torr to about 500 Torr, about 50 Torr to about500 Torr, about 6 Torr to about 100 Torr, about 20 Torr to about 100Torr, about 30 Torr to about 100 Torr, about 20 Torr to about 50 Torr,or about 20 Torr to about 30 Torr.

In some embodiments, the one or more plasma steps in a high-pressuretreatment sub-cycle can be free or substantially free of hydrogen ions(e.g., H⁺ and/or H³⁺ ions). For example, no or substantially nohydrogen-containing gas (e.g., hydrogen (H₂) gas) is flowed to thereaction chamber during the one or more plasma steps. A high-pressuretreatment sub-cycle comprising plasma steps free or substantially freeof energetic hydrogen ions may advantageously reduce or preventdelamination of deposited silicon nitride from the substrate. In someembodiments, no or substantially no hydrogen-containing gas is flowed tothe reaction chamber throughout the high-pressure treatment sub-cycle.

In some alternative embodiments, the one or more plasma steps in ahigh-pressure treatment sub-cycle can include hydrogen-containingspecies. For example, one or more plasma steps can include a plasmagenerated from hydrogen-containing components.

In some embodiments, a plasma power for a plasma step in a high-pressuretreatment sub-cycle can be about 100 Watts (W) to about 1,500 W,preferably from about 200 W to about 1,000 W, more preferably from about500 W to about 1,000 W. For example, a high-pressure treatment processmay have a plasma power of about 800 W.

In some embodiments, a PEALD process for depositing SiN can be performedusing plasma generated by capacitively coupled parallel plates, whichcan generate anisotropic ion bombardment upon the substrate, for exampleproviding a film having non-uniform characteristics on horizontal andvertical surfaces. For example, the film thicknesses and film quality onsubstrate top surfaces and sidewall surfaces may be significantlydifferent. The unevenness of the film thicknesses and film quality maybe further enhanced upon formation of re-entrant profile onthree-dimensional features of the substrate during deposition of theSiN, the re-entrant profile shadowing a sidewall portion (e.g., asidewall portion of a trench structure) from ion bombardment. In someembodiments, performing one or more of the high-pressure treatmentsub-cycle after one or more silicon nitride deposition sub-cycles canprovide SiN thin films having desired uniformity in film characteristicsof film formed on vertical and horizontal surfaces.

FIGS. 3A and 3B illustrate schematically examples of ion incident anglesdemonstrated by ions generated in a lower pressure plasma as compared toions generated by a higher pressure plasma. As used herein, ion incidentangle values, Θ₁ and Θ₂, are full width at half maximum (FWHM) values ofthe ion incident angle distribution. As described herein, a processpressure of the higher pressure plasma step can be greater than about 6Torr, for example about about 6 Torr to about 50 Torr, about 20 Torr toabout 50 Torr, about 6 Torr to about 500 Torr, or about 20 Torr to about500 Torr, including about 30 Torr to about 100 Torr. In someembodiments, a process pressure of the lower pressure plasma step can beless than 6 Torr, for example from about 0.1 Torr to about 5 Torr. FIG.3A shows an example ion incident angle Θ₁ of an ion generated in a lowerpressure plasma and FIG. 3B shows an example ion incident angle Θ₂ of anion generated in a higher pressure plasma. Ion incident angle Θ₂ can begreater than ion incident angle Θ₁. For example, a higher pressureplasma may generate a greater number of ion collisions in a plasmasheath region over the substrate, providing increased ion incident angleupon vertical surfaces of the substrate.

In some embodiments, the conditions of plasma step are selected toprovide an ion incident angle values of more than about 20°, includingmore than about 50°, or more than about 75°. In some embodiments, suchincident angle values are achieved in three-dimensional structureshaving aspect ratios of greater than about 2, aspect ratios greater thanabout 3, aspect ratios greater than about 5, and in some embodiments inaspect ratios of greater than about 8.

A plasma step performed in an elevated pressure regime mayadvantageously facilitate formation of a conformal SiN thin film havingdesired uniformity in characteristics between the film formed onhorizontal surfaces of the three-dimensional structure (e.g., a topsurface) and film formed on vertical surfaces of the three-dimensionalstructure. In some embodiments, increased ion incident angles canadvantageously provide improved uniformity in the wet etch rates and/orfilm thicknesses of SiN film formed on horizontal surfaces and verticalsurfaces of a three-dimensional structure. In some embodiments,increased ion incident angles can advantageously provide SiN thin filmshaving desired uniformity in film density and/or impurity levels betweenfilm formed on horizontal and vertical surfaces.

In some embodiments, a high-pressure treatment sub-cycle can include oneor more steps during which the substrate is not exposed to a plasma,such as one or more steps in which the substrate is transported to aspace free or substantially free of plasma radicals, and/or one or morepurge steps. In some embodiments, a purge step can precede a plasma stepin a high-pressure treatment sub-cycle. In some embodiments, a purgestep can follow a plasma step in a high-pressure treatment sub-cycle. Insome embodiments, a plasma step in a high-pressure treatment sub-cycleis both preceded and followed by a purge step. For example, ahigh-pressure treatment sub-cycle may include a first purge step,followed by a plasma step, and then a second purge step following theplasma step.

In some embodiments, a purge gas for the purge step comprises thecarrier gas. In some embodiments, a purge gas for the purge stepcomprises the nitrogen-containing gas used in a plasma step of thehigh-pressure treatment sub-cycle. In some embodiments, the carrier gasand the nitrogen-containing gas can be continuously flowed throughoutthe high-pressure treatment sub-cycle. For example, the flow of thecarrier gas and nitrogen-containing gas can be initiated for a firstpurge step. The flow of the carrier gas and nitrogen-containing gas maybe maintained or substantially maintained during a subsequent plasmastep, and the plasma power is turned on. The plasma power may be turnedoff after a desired duration, and the flow of the carrier gas andnitrogen-containing gas can be maintained after the plasma power isturned off and during the second purge step following the plasma step.

In some embodiments, a process pressure of the high-pressure treatmentsub-cycle may be increased during a purge step prior to a plasma stepand decreased in a purge step following the plasma step. For example, apressure of the reaction chamber may be ramped up during the purge stepto a desired pressure of the subsequent plasma step such that the plasmastep begins at the desired process pressure. The desired processpressure is maintained or substantially maintained during the plasmastep. The reaction chamber pressure may then be ramped down to a lowerpressure during the purge step following the plasma step. In someembodiments, the process pressure of the high-pressure treatmentsub-cycle can be maintained at a desired process pressure for a plasmastep of the sub-cycle.

In some embodiments, a purge step following a plasma step can includeflow of one or more gases used in a first step of a subsequent siliconnitride deposition sub-cycle. For example, a purge step performed aftera plasma step of a high pressure treatment sub-cycle and before asilicon nitride deposition sub-cycle can include flow of one or moregasses used a first step of the subsequent silicon nitride depositionsub-cycle. In some embodiments, the purge step can include flow ofhydrogen gas (H₂). For example, the purge step can include flow ofhydrogen gas (H₂) at a rate used for the subsequent silicon nitridedeposition sub-cycle step such that the flow of the hydrogen gas (H₂) ismaintained or substantially maintained at that rate for the first stepof the silicon nitride deposition sub-cycle. For example, the purge stepcan include flow of the carrier gas and nitrogen-containing gas (e.g.,N₂ gas), as well as hydrogen gas (H₂).

FIGS. 4A and 4B show examples of timing diagrams of various processparameters for a silicon nitride deposition sub-cycle and ahigh-pressure treatment sub-cycle. In the silicon nitride depositionsub-cycle shown in FIG. 4A, the silicon nitride deposition sub-cycle cancomprise a PEALD type process. For example, the silicon nitridedeposition sub-cycle may comprise a silicon precursor step (e.g., flowof one or more silicon precursors to the reaction chamber), followed bya purge step, then a plasma step comprising flow of nitrogen gas (N₂)and hydrogen gas (H₂), and another purge step. The silicon nitridedeposition sub-cycle may comprise alternating and sequentiallycontacting the substrate with the one or more silicon precursors (e.g.,by pulsing of the one or more silicon precursors) and the one or morenitrogen reactants (e.g., by application of the plasma step). Flow of acarrier gas and one or more gasses used for the plasma step (e.g.,nitrogen gas (N₂) and hydrogen gas (H₂)) can be continued for theduration of the sub-cycle. As described herein, the silicon nitridedeposition sub-cycle can be performed at a process pressuresignificantly lower than that used in a high-pressure treatment process.

As shown in FIG. 4A, the silicon precursor step can include starting andthen stopping flow of the one or more silicon precursors (e.g., pulsingthe one or more silicon precursors). The silicon precursor step may alsoinclude flow of a carrier gas, for example to facilitate delivery of theone or more silicon precursors to the substrate. In some embodiments,the carrier gas is Ar or comprises Ar. The silicon precursor step maycomprise flow of nitrogen gas (N₂) and hydrogen gas (H₂). In someembodiments, nitrogen gas (N₂) and hydrogen gas (H₂) can be flowedcontinuously or substantially continuously throughout the siliconnitride deposition sub-cycle.

The silicon precursor step may be followed by a first purge step toremove excess silicon precursors from the vicinity of the substrate. Thefirst purge step may comprise flow of the carrier gas and the nitrogengas (N₂) and hydrogen gas (H₂). As show in FIG. 4A, the siliconprecursor is not flowed during the purge step, while flow of the carriergas, the nitrogen gas (N₂) and hydrogen gas (H₂) can be continued. Forexample, flow of the carrier gas and the nitrogen gas (N₂) and hydrogengas (H₂) can be maintained or substantially maintained throughout thefirst purge step at a rate flowed used in the silicon precursor step.

The first purge step can be followed by the plasma step. As shown inFIG. 4A, the carrier gas may be flowed during the plasma step, forexample to facilitate delivery of the one or more nitrogen reactants tothe substrate such that the nitrogen reactants can react with theadsorbed silicon precursors. The plasma step can include turning on andthen turning off the plasma while flowing the carrier gas, and thenitrogen gas (N₂) and hydrogen gas (H₂) gas. For example, after a firstpurge step has been performed, the plasma step may include striking theplasma while maintaining or substantially maintaining the flow of thecarrier gas and the nitrogen gas (N₂) and hydrogen gas (H₂) at a rateused during the first purge step. The plasma step can be configured togenerate a plasma comprising N*, H*, NH* and/or NH₂* radicals.

The plasma power may be turned off after desired plasma has beenprovided and a second purge step can follow. As shown in the example ofFIG. 4A, flow of the carrier gas and the nitrogen gas (N₂) and hydrogengas (H₂) can be continued during the second purge step to remove excessreactants and/or reaction byproducts. For example, flow of the carriergas and the nitrogen gas (N₂) and hydrogen gas (H₂) may be maintainedduring the second purge step at a rate used in the plasma step. In someembodiments, flow of the carrier gas and the nitrogen gas (N₂) andhydrogen gas (H₂) can be maintained or substantially maintained a samerate throughout the silicon nitride deposition sub-cycle.

FIG. 4B shows an example of a timing diagram of various processparameters for a high-pressure treatment sub-cycle. As shown in FIG. 4B,silicon precursors are not provided during the high-pressure treatmentsub-cycle. According to the example shown in FIG. 4B, the high-pressuretreatment sub-cycle may comprise a first purge step, followed by aplasma step, and then a second purge step. The first purge step maycomprise flow of a carrier gas and nitrogen gas (N₂). Any flow ofhydrogen gas (H₂) can be turned off during the first purge step, forexample if hydrogen gas (H₂) was flowed for a step in an immediatelypreceding silicon nitride deposition sub-cycle, such that ahigh-pressure treatment sub-cycle free or substantially free of hydrogenions (e.g., H⁺ and/or H³⁺ ions) can be provided. Process pressure may beincreased during the first purge step. For example, the process pressuremay be ramped from an initial lower pressure (e.g., a pressure of animmediately preceding silicon nitride deposition sub-cycle or animmediately preceding high pressure treatment sub-cycle) to a desiredpressure of the subsequent plasma step.

The first purge step in the high pressure treatment sub-cycle can befollowed by the plasma step. Flow of the nitrogen gas (N₂) and thecarrier gas can be continued during the plasma step. For example, in theplasma step, plasma power is provided while nitrogen gas (N₂) and thecarrier gas are flowed, such as at a rate flowed during the first purgestep. The The nitrogen gas (N₂) can be used to generate a plasmacomprising non-reactive ions. The plasma may be turned off after desiredexposure of the substrate to the plasma, and the second purge step canbe performed.

Flow of the nitrogen gas (N₂) and the carrier gas can be continuedduring the second purge step. For example, flow of the nitrogen gas (N₂)and the carrier gas can be maintained at a rate used in the plasma step.In some embodiments, flow of the nitrogen gas (N₂) and the carrier gascan be maintained or substantially maintained a same rate throughout thehigh-pressure treatment sub-cycle. The process pressure may be decreasedduring the second purge step. For example, a pressure within thereaction chamber to which the substrate is exposed may be ramped downduring the second purge step from the process pressure of the plasmastep to a lower pressure.

In some embodiments, as shown in FIG. 4B, hydrogen gas (H₂) may beturned on during the second purge step. For example, the hydrogen gas(H₂) may be turned on if the high-pressure treatment sub-cycle isimmediately followed by a silicon nitride deposition sub-cyclecomprising flow of hydrogen gas (H₂).

In some embodiments, a process for forming a SiN thin film may comprisea plurality of super cycles, each super-cycle comprising a number ofrepetitions of the silicon nitride deposition sub-cycle of FIG. 4Afollowed by a number of repetitions of the high-pressure treatmentsub-cycle of FIG. 4B. The number of super-cycles, silicon nitridedeposition sub-cycles, and/or high-pressure treatment sub-cycles can beselected to form a SiN thin film having one or more desiredcharacteristics as described herein.

Si Precursors

In some embodiments, the Si precursor for depositing SiN thin filmcomprises a silyl halide. In some embodiments, the Si precursorcomprises iodine. In certain embodiments, the Si precursor is H₂SiI₂.

Examples of silicon precursors for depositing SiN are provided in U.S.patent application Ser. No. 14/167,904, filed Jan. 29, 2014, entitled“Si PRECURSORS FOR DEPOSITION OF SiN AT LOW TEMPERATURES,” which isincorporated herein by reference in its entirety.

In some embodiments, the Si-precursor comprises iodine and one or moreligands such as one or more organic ligands. In some embodiment, theSi-precursor may comprise iodine and one or more alkyl groups, such as amethyl group, ethyl group, propyl group, and/or hydrogen. In someembodiments, the Si-precursor comprises iodine and one or more otherhalides, such as bromine or chlorine.

In some embodiments, a silicon precursor comprises three iodines and oneamine or alkylamine ligands bonded to silicon. In some embodimentssilicon precursor comprises one or more of the following: (SiI₃)NH₂,(SiI₃)NHMe, (SiI₃)NHEt, (SiI₃)NH^(i)Pr, (SiI₃)NH^(t)Bu, (SiI₃)NMe₂,(SiI₃)NMeEt, (SiI₃)NMe^(i)Pr, (SiI₃)NMe^(t)Bu, (SiI₃)NEt₂,(SiI₃)NEt^(i)Pr, (SiI₃)NEt^(t)Bu, (SiI₃)N^(i)Pr₂, (SiI₃)N^(i)Pr^(t)Bu,and (SiI₃)N^(t)Bu₂. In some embodiments, a silicon precursor comprisestwo, three, four, five, six, seven, eight, nine, ten, eleven, twelve,thirteen, fourteen, fifteen or more compounds selected from (SiI₃)NH₂,(SiI₃)NHMe, (SiI₃)NHEt, (SiI₃)NH^(i)Pr, (SiI₃)NH^(t)Bu, (SiI₃)NMe₂,(SiI₃)NMeEt, (SiI₃)NMe^(i)Pr, (SiI₃)NMe^(t)Bu, (SiI₃)NEt₂,(SiI₃)NEt^(i)Pr, (SiI₃)NEt^(t)Bu, (SiI₃)N^(i)Pr₂, (SiI₃)N^(i)Pr^(t)Bu,(SiI₃)N^(t)Bu₂, and combinations thereof. In some embodiments, a siliconprecursor comprises two iodines and two amine or alkylamine ligandsbonded to silicon. In some embodiments, silicon precursor comprises oneor more of the following: (SiI₂)(NH₂)₂, (SiI₂)(NHMe)₂, (SiI₂)(NHEt)₂,(SiI₂)(NH^(i)Pr)₂, (SiI₂)(NH^(t)Bu)₂, (SiI₂)(NMe₂)₂, (SiI₂)(NMeEt)₂,(SiI₂)(NMe^(i)Pr)₂, (SiI₂)(NMe^(t)Bu)₂, (SiI₂)(NEt₂)₂,(SiI₂)(NEt^(i)Pr)₂, (SiI₂)(NEt^(t)Bu)₂, (SiI₂)(N^(i)Pr₂)₂,(SiI₂)(N^(i)Pr^(t)Bu)₂, and (SiI₂)(N^(t)Bu)₂. In some embodiments, asilicon precursor comprises two, three, four, five, six, seven, eight,nine, ten, eleven, twelve, thirteen, fourteen, fifteen or more compoundsselected from (SiI₂)(NH₂)₂, (SiI₂)(NHMe)₂, (SiI₂)(NHEt)₂,(SiI₂)(NH^(i)Pr)₂, (SiI₂)(NH^(t)Bu)₂, (SiI₂)(NMe₂)₂, (SiI₂)(NMeEt)₂,(SiI₂)(NMe^(i)Pr)₂, (SiI2)(NMe^(t)Bu)₂, (SiI₂)(NEt₂)₂,(SiI₂)(NEt^(i)Pr)₂, (SiI₂)(NEt^(t)Bu)₂, (SiI₂)(N^(i)Pr₂)₂,(SiI₂)(N^(i)Pr^(t)Bu)₂, (SiI₂)(N^(t)Bu)₂, and combinations thereof.

In certain embodiments, a silicon precursor comprises two iodines,hydrogen and one amine or alkylamine ligand or two iodines and twoalkylamine ligands bonded to silicon and wherein amine or alkylamineligands are selected from amine NH₂—, methylamine MeNH—, dimethylamineMe₂N—, ethylmethylamine EtMeN—, ethylamine EtNH—, and diethylamineEt₂N—. In some embodiments silicon precursor comprises one or more ofthe following: (SiI₂H)NH₂, (SiI₂H)NHMe, (SiI₂H)NHEt, (SiI₂H)NMe₂,(SiI₂H)NMeEt, (SiI₂H)NEt₂, (SiI₂)(NH₂)₂, (SiI₂)(NHMe)₂, (SiI₂)(NHEt)₂,(SiI₂)(NMe₂)₂, (SiI₂)(NMeEt)₂, and (SiI₂)(NEt₂)₂. In some embodiments asilicon precursor comprises two, three, four, five, six, seven, eight,nine, ten, eleven, twelve or more compounds selected from (SiI₂H)NH₂,(SiI₂H)NHMe, (SiI₂H)NHEt, (SiI₂H)NMe₂, (SiI₂H)NMeEt, (SiI₂H)NEt₂,(SiI₂)(NH₂)₂, (SiI₂)(NHMe)₂, (SiI₂)(NHEt)₂, (SiI₂)(NMe₂)₂,(SiI₂)(NMeEt)₂, (SiI₂)(NEt₂)₂, and combinations thereof.

In some embodiments, a silicon precursor comprises one or more of thefollowing: SiI₄, HSiI₃, H2SiI₂, H₃SiI, Si₂I₆, HSi₂I₅, H₂Si₂I₄, H₃Si₂I₃,H₄Si₂I₂, H5Si2I, Si3I8, HSi2I5, H2Si2I4, H3Si2I3, H4Si2I2, H5Si2I,MeSiI3, Me2SiI2, Me3SiI, MeSi2I5, Me2Si2I4, Me3Si2I3, Me4Si2I2, Me5Si2I,HMeSiI2, HMe2SiI, HMeSi2I4, HMe2Si2I3, HMe3Si2I2, HMe4Si2I, H2MeSiI,H2MeSi2I3, H2Me2Si2I2, H2Me3Si2I, H3MeSi2I2, H3Me2Si2I, H4MeSi2I,EtSiI3, Et2SiI2, Et3SiI, EtSi2I5, Et2Si2I4, Et3Si2I3, Et4Si2I2, Et5Si2I,HEtSiI2, HEt2SiI, HEtSi2I4, HEt2Si2I3, HEt3Si2I2, HEt4Si2I, H2EtSiI,H2EtSi2I3, H2Et2Si2I2, H2Et3Si2I, H3EtSi2I2, H3Et2Si2I, and H4EtSi2I.

In some embodiments, a silicon precursor comprises one or more of thefollowing: EtMeSiI2, Et2MeSiI, EtMe2SiI, EtMeSi2I4, Et2MeSi2I3,EtMe2Si2I3, Et3MeSi2I2, Et2Me2Si2I2, EtMe3Si2I2, Et4MeSi2I, Et3Me2Si2I,Et2Me3Si2I, EtMe4Si2I, HEtMeSiI, HEtMeSi2I3, HEt2MeSi2I2, HEtMe2Si2I2,HEt3MeSi2I, HEt2Me2Si2I, HEtMe3Si2I, H2EtMeSi2I2, H2Et2MeSi2I,H2EtMe2Si2I, H3EtMeSi2I.

In some embodiments, a silicon precursor comprises one iodine, onehydrogen and two amine or alkylamine ligand bonded to silicon. In someembodiments, silicon precursor comprises one or more of the following:(SiIH)(NH2)2, (SiIH)(NHMe)2, (SiIH)(NHEt)2, (SiIH)(NHiPr)2,(SiIH)(NHtBu)2, (SiIH)(NMe2)2, (SiIH)(NMeEt)2, (SiIH)(NMeiPr)2,(SiIH)(NMetBu)2, (SiIH)(NEt2)2, (SiIH)(NEtiPr)2, (SiIH)(NEttBu)2,(SiIH)(NiPr2)2, (SiIH)(NiPrtBu)2, and (SiIH)(NtBu)2. In someembodiments, a silicon precursor comprises two, three, four, five, six,seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen ormore compounds selected from (SiIH)(NH2)2, (SiIH)(NHMe)2, (SiIH)(NHEt)2,(SiIH)(NHiPr)2, (SiIH)(NHtBu)2, (SiIH)(NMe2)2, (SiIH)(NMeEt)2,(SiIH)(NMeiPr)2, (SiIH)(NMetBu)2, (SiIH)(NEt2)2, (SiIH)(NEtiPr)2,(SiIH)(NEttBu)2, (SiIH)(NiPr2)2, (SiIH)(NiPrtBu)2, and (SiIH)(NtBu)2,and combinations thereof.

In some embodiments, a silicon precursor comprises one iodine, twohydrogens and one amine or alkylamine ligand bonded to silicon. In someembodiments silicon precursor comprises one or more of the following:(SiIH2)NH2, (SiIH2)NHMe, (SiIH2)NHEt, (SiIH2)NHiPr, (SiIH2)NHtBu,(SiIH2)NMe2, (SiIH2)NMeEt, (SiIH2)NMeiPr, (SiIH2)NMetBu, (SiIH2)NEt2,(SiIH2)NEtiPr, (SiIH2)NEttBu, (SiIH2)NiPr2, (SiIH2)NtPrtBu, and(SiIH2)NtBu2. In some embodiments a silicon precursor comprises two,three, four, five, six, seven, eight, nine, ten, eleven, twelve,thirteen, fourteen, fifteen or more compounds selected from (SiIH2)NH2,(SiIH2)NHMe, (SiIH2)NHEt, (SiIH2)NHiPr, (SiIH2)NHtBu, (SiIH2)NMe2,(SiIH2)NMeEt, (SiIH2)NMeiPr, (SiIH2)NMetBu, (SiIH2)NEt2, (SiIH2)NEtiPr,(SiIH2)NEttBu, (SiIH2)NiPr2, (SiIH2)NiPrtBu, (SiIH2)NtBu2, andcombinations thereof.

In some embodiments, a silicon precursor comprises one iodine and threeamine or alkylamine ligands bonded to silicon. In some embodiments,silicon precursor comprises one or more of the following: (SiI)(NH2)3,(SiI)(NHMe)3, (SiI)(NHEt)3, (SiI)(NHiPr)3, (SiI)(NHtBu)3, (SiI)(NMe2)3,(SiI)(NMeEt)3, (SiI)(NMeiPr)3, (SiI)(NMetBu)3, (SiI)(NEt2)3,(SiI)(NEtiPr)3, (SiI)(NEttBu)3, (SiI)(NiPr2)3, (SiI)(NiPrtBu)3, and(SiI)(NtBu)3. In some embodiments a silicon precursor comprises two,three, four, five, six, seven, eight, nine, ten, eleven, twelve,thirteen, fourteen, fifteen or more compounds selected from (SiI)(NH2)3, (SiI)(NHMe)3, (SiI)(NHEt)3, (SiI)(NHiPr)3, (SiI)(NHtBu)3,(SiI)(NMe2)3, (SiI)(NMeEt)3, (SiI)(NMeiPr)3, (SiI)(NMetBu)3,(SiI)(NEt2)3, (SiI)(NEtiPr)3, (SiI)(NEttBu)3, (SiI)(NiPr2)3,(SiI)(NiPrtBu)3, (SiI)(NtBu)3, and combinations thereof.

In certain embodiments, a silicon precursor comprises two iodines,hydrogen and one amine or alkylamine ligand or two iodines and twoalkylamine ligands bonded to silicon and wherein amine or alkylamineligands are selected from amine NH2-, methylamine MeNH—, dimethylamineMe2N—, ethylmethylamine EtMeN—, ethylamine EtNH—, and diethylamineEt2N—. In some embodiments silicon precursor comprises one or more ofthe following: (SiI2H)NH2, (SiI2H)NHMe, (SiI2H)NHEt, (SiI2H)NMe2,(SiI2H)NMeEt, (SiI2H)NEt2, (SiI2)(NH2)2, (SiI2)(NHMe)2, (SiI2)(NHEt)2,(SiI2)(NMe2)2, (SiI2)(NMeEt)2, and (SiI2)(NEt2)2. In some embodiments asilicon precursor comprises two, three, four, five, six, seven, eight,nine, ten, eleven, twelve or more compounds selected from (SiI2H)NH2,(SiI2H)NHMe, (SiI2H)NHEt, (SiI2H)NMe2, (SiI2H)NMeEt, (SiI2H)NEt2,(SiI2)(NH2)2, (SiI2)(NHMe)2, (SiI2)(NHEt)2, (SiI2)(NMe2)2,(SiI2)(NMeEt)2, (SiI2)(NEt2)2, and combinations thereof.

N Precursors

As discussed above, the second reactant for depositing silicon nitrideaccording to the present disclosure may comprise a nitrogen precursor,which may comprise a reactive species. Suitable plasma compositions of aPEALD process include nitrogen plasma, radicals of nitrogen, or atomicnitrogen in one form or another. In some embodiments, hydrogen plasma,radicals of hydrogen, or atomic hydrogen in one form or another are alsoprovided. And in some embodiments, a plasma may also contain noblegases, such as He, Ne, Ar, Kr and Xe, preferably Ar or He, in plasmaform, as radicals, or in atomic form. In some embodiments, the secondreactant does not comprise any species from a noble gas, such as Ar.Thus, in some embodiments plasma is not generated in a gas comprising anoble gas.

Thus, in some embodiments the second reactant may comprise plasma formedfrom compounds having both N and H, such as NH₃ and N₂H₄, a mixture ofN₂/H₂ or other precursors having an N—H bond. In some embodiments thesecond reactant may be formed, at least in part, from N₂. In someembodiments the second reactant may be formed, at least in part, from N₂and H₂, where the N₂ and H₂ are provided at a flow ratio (N₂/H₂) fromabout 20:1 to about 1:20, preferably from about 10:1 to about 1:10, morepreferably from about 5:1 to about 1:5 and most preferably from about1:2 to about 4:1, and in some cases 1:1. For example, anitrogen-containing plasma for depositing silicon nitride can begenerated using both N₂ and H₂ at one or more ratios described herein.

In some embodiments, the nitrogen plasma may be free or substantiallyfree of hydrogen-containing species (e.g., hydrogen ions, radicals,atomic hydrogen). For example, hydrogen-containing gas is not used togenerate the nitrogen plasma. In some embodiments, hydrogen-containinggas (e.g., H₂ gas) is not flowed into the reaction chamber during thenitrogen plasma step.

In some embodiments, a plasma power used for generating anitrogen-containing plasma can be about 10 Watts (W) to about 2,000 W,about 50 W to about −1000 W, about 100 W to about 1000 W or about 500 Wto about 1000 W. In some embodiments, a plasma power used for generatinga nitrogen-containing plasma can be about 800 W to about 1,000 W.

The second reactant may be formed in some embodiments remotely viaplasma discharge (“remote plasma”) away from the substrate or reactionspace. In some embodiments, the second reactant may be formed in thevicinity of the substrate or directly above substrate (“direct plasma”).

SiN Film Characteristics

Silicon nitride thin films deposited according to some of theembodiments discussed herein may achieve impurity levels orconcentrations below about 3 at-%, preferably below about 1 at-%, morepreferably below about 0.5 at-%, and most preferably below about 0.1at-%. In some thin films, the total impurity level excluding hydrogenmay be below about 5 at-%, preferably below about 2 at-%, morepreferably below about 1 at-%, and most preferably below about 0.2 at-%.And in some thin films, hydrogen levels may be below about 30 at-%,preferably below about 20 at-%, more preferably below about 15 at-%, andmost preferably below about 10 at-%.

In some embodiments, the deposited SiN films do not comprise anappreciable amount of carbon. However, in some embodiments a SiN filmcomprising carbon is deposited. For example, in some embodiments an ALDreaction is carried out using a silicon precursor comprising carbon anda thin silicon nitride film comprising carbon is deposited. In someembodiments a SiN film comprising carbon is deposited using a precursorcomprising an alkyl group or other carbon-containing ligand. Differentalkyl groups, such as Me or Et, or other carbon-containing ligands mayproduce different carbon concentrations in the films because ofdifferent reaction mechanisms. Thus, different precursors can beselected to produce different carbon concentration in deposited SiNfilms. In some embodiments, a SiN film comprising carbon having desireddielectric constant can be deposited. In some embodiments the thin SiNfilm comprising carbon may be used, for example, as a low-k spacer. Insome embodiments the thin films do not comprise argon.

According to some embodiments, the silicon nitride thin films mayexhibit step coverage and pattern loading effects of greater than about50%, preferably greater than about 80%, more preferably greater thanabout 90%, and most preferably greater than about 95%. In some casesstep coverage and pattern loading effects can be greater than about 98%and in some case about 100% (within the accuracy of the measurement toolor method). These values can be achieved in features with aspect ratiosof 2 or greater, in some embodiments in aspect ratios of about 3 orgreater, in some embodiments in aspect ratios of about 5 or greater andin some embodiments in aspect ratios of about 8 or greater.

As used herein, “pattern loading effect” is used in accordance with itsordinary meaning in this field. While pattern loading effects may beseen with respect to impurity content, density, electrical propertiesand etch rate, unless indicated otherwise the term pattern loadingeffect when used herein refers to the variation in film thickness in anarea of the substrate where structures are present. Thus, the patternloading effect can be given as the film thickness in the sidewall orbottom of a feature inside a three-dimensional structure relative to thefilm thickness on the sidewall or bottom of the three-dimensionalstructure/feature facing the open field. As used herein, a 100% patternloading effect (or a ratio of 1) would represent about a completelyuniform film property throughout the substrate regardless of featuresi.e. in other words there is no pattern loading effect (variance in aparticular film property, such as thickness, in features vs. openfield).

In some embodiments, silicon nitride films are deposited to athicknesses of from about 3 nm to about 50 nm, preferably from about 5nm to about 30 nm, more preferably from about 5 nm to about 20 nm. Thesethicknesses can be achieved in feature sizes (width) below about 100 nm,preferably about 50 nm, more preferably below about 30 nm, mostpreferably below about 20 nm, and in some cases below about 15 nm.According to some embodiments, a SiN film is deposited on athree-dimensional structure and the thickness at a sidewall may beslightly even more than 10 nm.

According to some embodiments silicon nitride films with various wetetch rates (WER) may be deposited. When using a blanket WER in 0.5% dHF(nm/min), silicon nitride films may have WER values of less than about5, preferably less than about 4, more preferably less than about 2, andmost preferably less than about 1. In some embodiments it could lessthan about 0.3.

The blanket WER in 0.5% dHF (nm/min) relative to the WER of thermaloxide may be less than about 3, preferably less than about 2, morepreferably less than about 1, and most preferably less than about 0.5.

And in some embodiments, the sidewall WER of the three dimensionalfeature, such as fin or trench relative to the top region WER of a threedimensional feature, such as fin or trench, in 0.5% dHF may be less thanabout 4, preferably less than about 3, more preferably less than about2, most preferably about 1.

In some embodiments, SiN formed according to one or more processesdescribed herein can advantageously demonstrate a WERR of about 1, forexample in 0.5% dHF. For example, a ratio of a wet etch rate of SiN thinfilm formed over horizontal surfaces (e.g., top surfaces) to a wet etchrate of the SiN thin film formed over vertical surfaces (e.g., sidewallsurfaces) of three-dimensional structures on a substrate surface can bethe same or substantially the same. In some embodiments, the ratio canbe about 0.25 to about 2, about 0.5 to about 1.5, about 0.75 to about1.25, or about 0.9 to about 1.1. These ratios can be achieved infeatures with aspect ratios of about 2 or more, about 3 or more, about 5or more or even about 8 or more.

It has been found that in using the silicon nitride thin films of thepresent disclosure, thickness differences between top and side may notbe as critical for some applications, due to the improved film qualityand etch characteristics. Nevertheless, in some embodiments, thethickness gradient along the sidewall may be very important tosubsequent applications or processes.

In some embodiments, the amount of etching of silicon nitride filmsaccording to the present disclosure may be about one or two times lessthan amount of etching observed for thermal SiO₂ (TOX) in a 0.5% HF-dipprocess (for example in a process in which about 2 to about 3 nm TOX isremoved, one or two times less SiN is removed when deposited accordingto the methods disclosed herein). The WER of preferred silicon nitridefilms may be less than that of prior art thermal oxide films.

FIGS. 5A through 5C are wet etch rate (WER) curves showing example wetetch rate performances in dilute HF (0.5 weight % aqueous solution) ofSiN thin films deposited over three-dimensional trench structures. Thefilms were deposited using PEALD processes using H₂SiI₂ as the siliconprecursor and N₂ and H₂ gases for generating the reactivenitrogen-containing species. The wet etch rate is shown on the y-axis innanometers per minute (nm/min) and the plasma power used in thedeposition of the SiN thin film is shown on the x-axis in Watts (W). TheSiN films of FIGS. 5A through 5C were deposited on trench structureshaving an aspect ratio of about 3.

The SiN films of FIGS. 5A and 5B were deposited using a PEALD process ata process pressure of about 350 Pascals (Pa). WER curve 502 shows etchperformance of the portion of the SiN film formed on top surfaces of thetrench structures using the process pressure of about 350 Pa. WER curve504 shows etch performance of the portion of the SiN film formed onsidewall surfaces of the trench structures using the process pressure ofabout 350 Pa. FIG. 5B shows a portion of the WER curves 502, 504 shownin FIG. 5A.

FIGS. 5A and 5B show RF power dependency of wet etch rate performance ofSiN film deposited at the process pressure of about 350 Pa. For example,portions of SiN films deposited on top surfaces of the trench structuresat RF powers less than about 600 W demonstrated better wet etch rateperformance than that formed on sidewall surfaces of the trenches. Insome embodiments, such a difference in wet etch rate performance may bedue to less ion bombardment on the side wall surfaces of the trenchesthan on the top surfaces. In SiN films deposited using the processpressure of about 350 Pa, wet etch rate of the portions of the filmsformed on sidewall surfaces improved with increased RF power in thedeposition process, while that of the portions of the films formed ontop surfaces deteriorated. In some embodiments, such an improvement inwet etch rate of film formed on sidewall surfaces may be due, at leastin part, to increased density of ion species in higher RF powerprocesses. In some embodiments, the deterioration of wet etch rate offilm formed on top surfaces may be due, at least in part, degradation offilm quality on the top surfaces at higher RF powers, for example due toover exposure of the top surfaces to ion bombardment.

The SiN films of FIG. 5C were deposited using a PEALD process performedat a process pressure of about 3000 Pascals (Pa). WER curve 506 showsetch performance of the portions of the SiN films formed on top surfacesof the trench structures using the process pressure of about 3000 Pa.WER curve 508 shows etch performance of the portions of the SiN filmsformed on sidewall surfaces of the trench structures using the processpressure of about 3000 Pa.

As shown in FIG. 5C, higher RF power used in the higher pressure PEALDprocess improved the wet etch rate performance of SiN film formed onside wall surfaces, while desired wet etch rate performance of SiN filmformed on top surfaces of the trenches was maintained. In someembodiments, the higher pressure process may reduce effects on filmquality due to anisotropy of ion bombardment by increasing collision ofplasma species. As shown in FIG. 5C, using a higher pressure process mayprovide desired film wet etch rate performances of film formed both ontop and side wall surfaces. For example, wet etch rate of SiN filmportions formed on top and side wall surfaces can be improved from about0.50 nm/min to about 0.32 nm/min.

FIGS. 6A and 6B are scanning electron microscope (SEM) images showingcross-sectional views of SiN films formed on trench structures, prior toand after exposure to a 5 minute dip in dHF 100:1 wet etch solution,respectively. The SiN films of FIGS. 6A and 6B were formed according tothe process described with reference to FIG. 5A above.

FIGS. 6C and 6D are SEM images showing cross-sectional views of SiNfilms formed on trench structures, prior to and after exposure to a 5minute dip in dHF 100:1 wet etch solution, respectively, where the SiNfilms are formed according to the process described with reference toFIG. 5C above.

As shown in FIGS. 6A and 6C, the SiN film formed using the higherpressure PEALD process demonstrated improved conformality (e.g., aconformality value of about 92%) prior to the wet etch dip, as comparedto the SiN film formed using the lower pressure PEALD process (e.g., aconformality value of about 69%). As shown in FIGS. 6B and 6D, theconformality of the SiN thin film formed using the higher pressure PEALDprocess was maintained subsequent to the wet etch dip, while that of theSiN thin film formed using the lower pressure PEALD process wassignificantly decreased. Additionally, the SiN thin film formed usingthe higher pressure PEALD process demonstrated a wet etch rate ratio(WERR) of about 1, while the SiN thin film formed using the lowerpressure PEALD process demonstrated a WERR of about 1.55 to about 0.26(top surfaces to sidewall surfaces).

Specific Contexts for Use of SiN Films

The methods and materials described herein can provide films withincreased quality and improved etch properties not only for traditionallateral transistor designs, with horizontal source/drain (S/D) and gatesurfaces, but can also provide improved SiN films for use onnon-horizontal (e.g., vertical) surfaces, and on complexthree-dimensional (3D) structures. In certain embodiments, SiN films aredeposited by the disclosed methods on a three-dimensional structureduring integrated circuit fabrication. The three-dimensional transistormay include, for example, double-gate field effect transistors (DG FET),and other types of multiple gate FETs, including FinFETs. For example,the silicon nitride thin films of the present disclosure may be usefulin nonplanar multiple gate transistors, such as FinFETs, where it may bedesirable to form silicide on vertical walls, in addition to the tops ofthe gate, source, and drain regions.

Another 3D structure for which the SiN deposition techniques taughtherein are particularly useful is a 3D elevated source/drain structure,as taught in U.S. Patent Publication No. 2009/0315120 by Shifren et al.,the disclosure of which is incorporated herein by reference in itsentirety. Shifren et al. teach elevated source/drain structures thatinclude vertical sidewalls.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. The described features, structures,characteristics and precursors can be combined in any suitable manner.Therefore, it should be clearly understood that the forms of the presentinvention are illustrative only and are not intended to limit the scopeof the present invention. All modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

What is claimed is:
 1. A method of forming a silicon nitride thin filmon a substrate in a reaction space by a plasma enhanced atomic layerdeposition (PEALD) comprising: a plurality of first silicon nitridedeposition cycles comprising alternately and sequentially contacting thesubstrate with a first silicon precursor and a first nitrogen plasma ata first deposition pressure; a plurality of second silicon nitridedeposition cycles comprising alternately and sequentially contacting thesubstrate with a second silicon precursor and a second nitrogen plasmaat a second deposition pressure, wherein the second deposition pressureis different from the first deposition pressure; and a plurality ofhigh-pressure treatment cycles comprising contacting the substrate witha third nitrogen plasma at a treatment pressure 6 Torr to 50 Torr. 2.The method of claim 1, wherein the first deposition pressure is about 20Torr to about 30 torr.
 3. The method of claim 1, wherein the seconddeposition pressure is about 6 Torr to about 50 Torr.
 4. The method ofclaim 1, wherein at least one of the first silicon precursor and thesecond silicon precursor comprises iodine.
 5. The method of claim 1,wherein the first silicon precursor is H₂SiI₂.
 6. The method of claim 1,wherein the second silicon precursor is H₂SiI₂.
 7. The method of claim1, wherein one or more of the first, second, and third nitrogen plasmais generated from a nitrogen precursor selected from the groupconsisting of NH3, N2H4, an N2/H2 mixture, N2, and any mixtures thereof.8. The method of claim 1, wherein the silicon nitride thin film isdeposited on a three-dimensional structure on the substrate, and whereina wet etch rate ratio of a wet etch rate of a portion of the siliconnitride thin film formed on a top surface of the three-dimensionalstructure to a wet etch rate of a portion of the silicon nitride thinfilm formed on a sidewall surface of the three-dimensional structure isfrom about 0.75 to about 1.25 in dilute 0.5 weight % HF.
 9. The methodof claim 8, wherein the wet etch rate ratio of the wet etch rate of theportion of the silicon nitride thin film formed on the top surface ofthe three-dimensional structure to the wet etch rate of the portion ofthe silicon nitride thin film formed on the sidewall surface of thethree-dimensional structure is about 1:1 in the dilute 0.5 weight % HF.10. The method of claim 1, wherein the plurality of at least one of thefirst and second silicon nitride deposition cycles further comprisesflowing a carrier gas throughout the plurality of at least one of thefirst and second silicon nitride deposition cycles.
 11. The method ofclaim 10, wherein the plurality of at least one of the first and secondsilicon nitride deposition cycles further comprises flowing ahydrogen-containing gas and a nitrogen-containing gas throughout theplurality of the at least one of the first and second silicon nitridedeposition cycles.
 12. The method of claim 11, wherein thehydrogen-containing gas and the nitrogen-containing gas are used to format least one of the first and second nitrogen plasmas.
 13. A method offorming a silicon nitride thin film on a substrate in a reaction spacecomprising: depositing silicon nitride by a plurality of depositioncycles comprising alternately and sequentially contacting the substratewith H₂Si₂ and a first nitrogen plasma, wherein the plurality ofdeposition cycles is carried out at one of two different depositionpressures; and treating the deposited silicon nitride by contacting thesubstrate with a second nitrogen plasma at a treatment pressure 6 Torrto 50 Torr.
 14. The method of claim 13, wherein at least one of the twodifferent deposition pressures is about 6 Torr to about 50 Torr.
 15. Themethod of claim 13, wherein at least one of the two different depositionpressures is about 20 Torr to about 30 Torr.
 16. The method of claim 13,wherein at least one of the two different deposition pressures is about20 Torr.
 17. The method of claim 13, wherein the first and secondnitrogen plasmas are generated from a nitrogen precursor selected fromthe group consisting of NH3, N2H4, an N2/H2 mixture, N2, and anymixtures thereof.
 18. The method of claim 13, wherein the siliconnitride thin film is deposited on a three-dimensional structure on thesubstrate, and wherein a wet etch rate ratio of a wet etch rate of aportion of the silicon nitride thin film formed on a top surface of thethree-dimensional structure to a wet etch rate of a portion of thesilicon nitride thin film formed on a sidewall surface of thethree-dimensional structure is from about 0.75 to about 1.25 in dilute0.5 weight % HF.
 19. The method of claim 13, wherein the plurality ofdeposition cycles further comprises flowing a hydrogen-containing gasand a nitrogen-containing gas throughout the plurality of depositioncycles.
 20. The method of claim 19, wherein the hydrogen-containing gasand the nitrogen-containing gas are used to form the first and/or secondnitrogen plasma.